Modular lithium-ion battery system for fork lifts

ABSTRACT

Many embodiments involve rechargeable battery assemblies that are forklift-battery-sized but that comprise multiple removable battery modules. The removable battery modules are individually rechargeable and are interchangeable with each other. A housing contains six battery modules installed vertically on the front side of the assembly, with their electrical and data connections occurring within the housing on the rear side. Assemblies will be two sided so that the system has two racks with six modules per rack. The handles of each module are collapsible and on the top edges of the overall assembly so that they are readily accessible during removal. Each battery module has an integrated battery supervisor system (BSS). A Battery Operating System Supervisor (BOSS) module processor serves as a battery management system for the all the battery modules. The BOSS module grants permissions to battery modules to enable them to connect and disconnect from busbars at the appropriate times to prevent electrical issues.

CLAIM OF PRIORITY TO PRIOR APPLICATIONS

The present application claims the benefit of pending PCT application,PCT/US18/42188, filed on Jul. 13, 2018, previously filed U.S.Provisional Application Ser. No. 62/532,199, filed on Jul. 13, 2017, aswell as previously filed co-pending U.S. Provisional Application Ser.No. 62/692,702, filed on Jun. 30, 2018. By this reference, the fulldisclosures, including the claims and drawings, of PCT/US18/42188, U.S.Provisional Application Ser. Nos. 62/532,199 and 62/692,702, areincorporated herein as though now set forth in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to battery-powered industrial trucks andtheir rechargeable batteries, as well as to related aspects of theiruse. More particularly, the invention is most directly related to ClassI forklifts but may also find applicability in relation to other classesof battery-powered industrial trucks.

2. Description of Related Art

Before reviewing the particular field of the invention, it may behelpful to consider background information on rechargeable lithium-ionbatteries in general. Rechargeable lithium-ion batteries were developedin the 1970's, and many of their benefits and potential industrial useswere well understood even then. Although commercial adoption wasinitially slow, they became much more widely popular by the 1990's. Theyare principally characterized by reference to the type of intercalatedlithium compound used as the cathodes in their battery cells. Lithiummetal oxides have been the most successful, with lithium cobalt oxide(LCO, or LiCoO₂) being most popular for use in industry, although itsuse has not been without drawbacks, particularly with respect to thermalrunaway and related safety concerns. Through the course of development,substantial improvements have been realized by doping of lithium cathodeformulations with additional metals such as nickel, manganese, andaluminum. Various innovations have also involved core-shell particlecathodes, improved anodes, and the use of solid lithium polymerelectrolytes, and still other innovations have led to smaller cathodeparticle sizes, increased electrode surface areas, and otherimprovements in overall battery capacity.

Today, the most popular lithium-ion batteries are of the LCO type, withlithium nickel cobalt aluminum oxide (NCA, or LiNiCoAlO₂) and lithiumnickel manganese cobalt oxide (NMC, or LiNiMnCoO₂) being particularlypopular. Other alternative cathode compositions have included otherlithium metal oxides such as lithium manganese oxide (LMO) and lithiummanganese nickel oxide (LMNO), and other lithium-ion chemistries can beconsidered for particular needs. Lithium metal phosphates, for instance,have also long been theoretically available for improved cycle counts,shelf life, and safety, although other performance trade-offs have madethem less popular than LCO types amongst manufacturers. As oneparticular type of lithium metal phosphate, lithium iron phosphate (LFP,or LiFePO₄) batteries have long been known as an available type ofrechargeable lithium-ion battery, with various pros and cons relative toNCA, NMC and other LCO batteries, which have generally weighed againstuse of LFP.

As a particular example of successful implementation of lithium-ionbatteries in other fields, Tesla, Inc. has popularized the use of NCAbatteries for its Model S electric cars. Their NCA batteries work welllargely due to their high energy density, although they tend to haverelatively low thermal stability, with a thermal runaway temperature ofaround 150° C. Tesla's battery manufacturing method helps balance thebenefits and risks by safely interconnecting hundreds of smaller batterycells in a much larger assembly, in a way that enables the necessaryenergy density while minimizing the risk of arcing and overheating.Within the larger assembly, the hundreds of smaller battery cells areconnected in groups, each group including a parallel arrangement ofnumerous cells connected by wire bonds to adjacent busbars. The busbarsof those groups are then combined in series to produce a much largerassembly that meets the power demands for an electric car. The methodpermanently connects each terminal of each cell into the overallassembly, although rather than using traditional methods of soldering,resistive spot welding, or laser welding, Tesla uses ultrasonicvibration welding, and the wire bonds are made of low resistance wirethat allows for expected currents to pass through without significantoverheating. Each wire bond is only about a centimeter in length, withone end bonded to the battery terminal and the other end bonded to analuminum busbar conductor, which in turn is electrically joined in acircuit with other busbars. In the event of overcurrent such as with ashort circuit or the like, each wire bond can serve as a fuse thatbreaks to prevent excessive overheating.

Although LFP batteries tend to have lower energy densities than NCA andNMC batteries, they have also long been known to have greater thermalstability. Thermal runaway for LFP batteries typically does not occuruntil around 270° C., which improves safety and decreases the likelihoodof catastrophic failure. LFP batteries are also more stable under shortcircuit or overcharge conditions and will not readily decompose at hightemperatures. As other arguable advantages, LFP batteries also tend tohave greater power density (i.e., they can source higher power levelsper unit volume) as well as greatly increased cycle life in comparisonto lead-acid batteries. While common lead-acid batteries have an averagelife of 300 cycles with 20% degradation of stored charge, LFP batteriescan last over 2000 cycles with the same 20% degradation of storedcharge.

Meanwhile in the field of the present invention, despite longavailability of lithium ion batteries in general, Class I forklifts arestill typically powered by lead-acid batteries. One reason is that manyforklifts, especially Class I forklifts, require a substantialcounterbalance for safe use. While lead-acid forklift batteries commonlyweigh more than a thousand pounds, many forklifts have therefore beendesigned to use the weight of lead-acid batteries to maintain stability.However, their massive weight also presents numerous challenges,particularly in the context of extracting, replacing and otherwisehandling them. While personnel cannot safely lift anything near thatheavy, special hoists and battery changing equipment are required, whichin turn involves more expense and floor space, not to mention the risksof back injury and the like.

Beyond the weight-related risks, because of the corrosive nature ofsulfuric acid, lead-acid batteries also present risks of damage to eyes,lungs, skin and clothing of personnel who work with them. Plus, hydrogengas is commonly released during battery recharge, which can combineexplosively with oxygen, as well as cause accelerated corrosion ofsurrounding components. Consequently, special safety protocols areneeded with lead acid batteries, and special attention is needed toensure adequate ventilation of hydrogen and sulfuric fumes aroundforklifts and their recharging stations.

Moreover, lead-acid forklift batteries are also expensive in terms oftime, space and inventory. A lead-acid forklift battery can generallyonly be used continuously for around six hours before requiring 8-9hours to recharge. They can also require extensive hours of maintenanceand have a much shorter life cycle when compared to lithium-iontechnologies. They also tend to require dedication of large areas inwarehouses for charging and maintenance, and each forklift generallyrequires two spare batteries for a facility conducting 24-houroperations.

As a result of many of the above-mentioned and other reasons, othershave long considered use of lithium-ion forklift batteries as analternative, but any resulting attempts have been weak at best, and manyof the challenges of the characteristically massive lead-acid forkliftbatteries still plague forklift-related industries.

Therefore, despite the well-known characteristics and long availabilityof rechargeable LFP and other lithium-ion battery technologies, thereare still substantial and long-felt unresolved needs for batterytechnology improvements in the forklift industry. Commonly owned U.S.Provisional Patent Application 62/532,199 is incorporated herein byreference in its entirety.

SUMMARY OF THE INVENTION

The innovations of the present invention improve safe and reliableoperations of conventional electric forklifts in various ways, in partby enabling rechargeable lithium-ion forklift batteries that areinterchangeable with lead-acid forklift batteries for which suchforklifts are conventionally adapted to be used. Many embodiments of thepresent invention involve rechargeable battery assemblies that areforklift-battery-sized but that comprise multiple removable batterymodules. The removable battery modules are individually rechargeable andare interchangeable with each other. Each such battery module isself-contained, is equipped with an integral handle for easy removalfrom the outer assembly, and is preferably sized and otherwise adaptedto be manually removable by forklift operators and maintenancepersonnel. Hence, each individual battery module can be selectivelyremoved for purposes of recharging it or replacing it with a fullycharged replacement module.

Preferred adaptations are such that, if the operator or maintenancepersonnel desires to recharge the entire assembly, that entire assemblycan be removed and recharged in the same manner as conventionallead-acid forklift batteries, or the preferred method of charging theentire assembly while it remains in the forklift; whereas one or more ofthe separately removable modules can alternatively be removed by handfor recharge or replacement. Aspects of the invention further allow forremoval of multiple modules out of the larger battery assembly, to allowfor its recharge or replacement, while still allowing continued forkliftoperation. Moreover, due to other innovative aspects of Applicant'sapproach, the individual battery modules and/or the larger assembly canbe recharged with lithium-ion chargers but are also readily compatibleto be recharged with conventional lead acid battery chargers.

Preferred embodiments of the larger battery assemblies include a housingthat is forklift-battery-sized, together with a symmetrical arrangementof individually removable and interchangeable modules. Preferably, thehousing contains six battery modules installed vertically on the frontside of the assembly, with their electrical and data connectionsoccurring within the housing on the rear side. Preferred embodimentswill be two sided so that the system has two racks with six modules perrack for a total of 12 modules. The handles of each module arecollapsible and oriented on the top edges of the overall assembly sothat they are readily accessible during manual removal of thecorresponding modules.

A preferred embodiment has battery modules secured in place using doorswith latches. Each battery module has a low friction surface to ensuresmooth and controlled movement during release of the battery modules.There is interlock functionality built into pins in a low voltageconnector. This interlock is wired so that three conditions must be metbefore the battery module will engage the communication bus. Theseconditions include mating of the low current connector, engagement ofthe physical locking system on the housing rack, and successful link tothe communication bus. The interlock pin loops through the physicallatch in the slot where the module connects so that the BOSS moduleknows that the module is connected. When a module is inserted and thelatch closes, the interlock pin is shorted with module ground pin. Thismechanism helps prevent arcing in many embodiments of the presentinvention. Without associated benefits, arcing might otherwise lead toovercurrent scenarios which, in turn, run the risk of causingdestruction of electrical connectors in the absence of propersafeguards.

Each battery module has an integrated battery supervisor system (BSS).The system monitors the health to include cell voltage, current, andtemperature. During charging, the system monitors the state of charge,compensates for voltage differences, and ensures the pack remainsoperational if and only if the battery cells are properly balanced andwithin the operating temperature limits. Additionally, the system canretain and communicate history and information to lift trucks andchargers through a physical CAN bus.

Battery modules of preferred embodiments are connected in a combinationof series and parallel to achieve higher voltage, higher capacity, andhigher ampacity. Each battery module is self-sufficient containing itsown internal controllers. However, there will be some redundantmonitoring and control conducted by secondary controllers, e.g. motorcontrollers and/or chargers.

Within each module, individual battery cells are connected using anapproach that is comparable to the Tesla method of wire bonded batterymanufacture. An important difference from Tesla, however, involves theuse of LFP battery technologies rather than NCA or other LCO batterytechnologies, as previously discussed. Amidst a number of resultingperformance differences, it is notable that in the preferred embodiment,removal of up to four modules per housing rack for charging still allowscontinued operation of the forklift, since such removal does notdecrease the voltage below the overall requirements. The assemblyrequires a minimum number of two 24 Volt battery modules for continuousoperation. Located between the battery cells and the printed circuitboard (PCB) are plastic battery trays and a thermally conductiveadhesive. A thermally conductive, electrically insulative adhesive isused between the top plastic battery tray and the PCB. Additionally, thesame adhesive is used between the battery cells and the top and bottomplastic battery trays. A thermal gap filler is applied between thebottom of the battery cells and the module enclosure for the purpose ofthermal management.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 shows a perspective view of a preferred embodiment of thedisclosed assembly with closed doors. The assembly includes a housingrack containing six separable battery modules.

FIG. 2 shows a side view of a Class I forklift in a configurationrepresentative of the prior art, showing its inclusion of a conventionallead-acid forklift battery in an openable battery compartment witharrows conceptually illustrating the relationship between itscounterweight, the weight of its load, and the resulting center of massin comparison to the force of the opposing fulcrum created at the frontwheels of the forklift.

FIG. 3 is a side view of a Class I forklift without the conventionallead acid forklift battery of FIG. 1, instead incorporating arechargeable battery assembly according to the teachings of the presentinvention.

FIG. 4A shows the disengagement of a slam latch from the housing.

FIG. 4B shows the pin locking feature of the door which holds thebattery module in place.

FIGS. 5A and 5B show a door of housing in a halfway open position andthe location of the door pin.

FIGS. 6A and 6B show a door of housing in a fully open position and thelocation of the door pin.

FIGS. 7A and 7B show the removal process for the module from the housingonce the door is fully opened.

FIGS. 8A and 8B show the disengagement of a slam latch from the housingfor an alternative embodiment.

FIGS. 9A and 9B show a door of housing in a halfway open position andthe location of the module pin.

FIGS. 10A and 10B show a door of housing in a fully open position andthe location of the module pin.

FIGS. 11A and 11B show the removal process for the module from thehousing once the door is fully opened.

FIG. 12 shows a rear view of the housing with the modules inserted.

FIG. 13 shows a perspective view of the rear and sides of the housingwith the modules inserted.

FIG. 14 shows a rear view of a battery module.

FIG. 15 shows a sectional front view of a battery module.

FIG. 16 shows a perspective view of the interior of a battery module.

FIG. 17 shows a top interior view of a battery module.

FIG. 18 shows a cross sectional view of an individual battery cellwithin a module.

FIG. 19 shows a schematic diagram where the six battery modules areconnected in parallel to the housing rack.

FIG. 20 is an elevation view of the rechargeable battery assembly 220 ofan alternative embodiment. The assembly 220 is a variation thatincorporates eight separable battery modules 330, while FIG. 15 showsthe outer housing rack 300 and one half of those eight battery modules330 (namely modules 330 a-330 d) operatively positioned therein.

FIG. 21 is a middle cross-section view of the rechargeable batteryassembly 220 of an alternative embodiment, showing the outer housingrack 300 and the other half of the battery modules 330 (i.e., the halfnot shown in FIG. 21, namely modules 330 e-330 h) operatively positionedtherein, with the viewing plane of FIG. 22 being numbered as thecross-sectional plane 4-4 in FIG. 23.

FIG. 22 is a partially-cut-away isometric perspective view of therechargeable battery assembly 220 of an alternative embodiment with itsbattery modules 330 operatively positioned therein, with a large portionof the top wall 303 and part of central wall 350 partially cut-away inorder to reveal some of its detail.

FIG. 23A is a partial isometric perspective view focusing on one of theindividual battery modules 330 (namely, module 330 a) of an alternativeembodiment in its operatively engaged position within bay 307 a ofhousing rack 300, with most of that housing being cut-away to show themodule 330 a and its removability in the direction of arrows 608 and609.

FIG. 23B is a simpler isometric view showing the rear of an individualbattery module 330 a of an alternative embodiment resting on elementalrepresentations of slides 610 and 611 of the housing rack assembly 300.

FIG. 24A is an isometric view of the top of the interior of a batterymodule 330 of an alternative embodiment and its rear connections 400,401 and 402.

FIG. 24B is an isometric view of the bottom of the interior of thebattery module 330 of the alternative embodiment of FIG. 24A, and itsrear connections 400, 401 and 402.

FIG. 25 is an elemental top view of a battery module 330 of analternative embodiment showing symbolic representations of itsconnections and mechanisms for operative installation and removal in andfrom the housing rack 300 of FIG. 23.

FIG. 26 is a schematic diagram example of an alternative embodiment withthe battery modules in the housing rack connected in parallel andconnected to a housing rack control system 901.

DETAILED DESCRIPTIONS OF PREFERRED EMBODIMENTS

The following descriptions relate to presently preferred embodiments andare not to be construed as describing limits to the invention, whereasthe broader scope of the invention should instead be considered withreference to the claims, which may be now appended or may later be addedor amended in this or related applications. Unless indicated otherwise,it is to be understood that terms used in these descriptions generallyhave the same meanings as those that would be understood by persons ofordinary skill in the art. It should also be understood that terms usedare generally intended to have the ordinary meanings that would beunderstood within the context of the related art, and they generallyshould not be restricted to formal or ideal definitions, conceptuallyencompassing equivalents, unless and only to the extent that aparticular context clearly requires otherwise.

For purposes of these descriptions, a few wording simplifications shouldalso be understood as universal, except to the extent otherwiseclarified in a particular context either in the specification or inparticular claims. The use of the term “or” should be understood asreferring to alternatives, although it is generally used to mean“and/or” unless explicitly indicated to refer to alternatives only, orunless the alternatives are inherently mutually exclusive. Whenreferencing values, the term “about” may be used to indicate anapproximate value, generally one that could be read as being that valueplus or minus half of the value. “A” or “an” and the like may mean oneor more, unless clearly indicated otherwise. Such “one or more” meaningsare most especially intended when references are made in conjunctionwith open-ended words such as “having,” “comprising” or “including.”Likewise, “another” object may mean at least a second object or more.

Preferred Embodiments

The following descriptions relate principally to preferred embodimentswhile a few alternative embodiments may also be referenced on occasion,although it should be understood that many other alternative embodimentswould also fall within the scope of the invention. It should beappreciated by those of ordinary skill in the art that the techniquesdisclosed in these examples are thought to represent techniques thatfunction well in the practice of various embodiments, and thus can beconsidered to constitute preferred modes for their practice. However, inlight of the present disclosure, those of ordinary skill in the artshould also appreciate that many changes can be made relative to thedisclosed embodiments while still obtaining a comparable function orresult without departing from the spirit and scope of the invention.

Housing Rack and Battery Module Interface Design

In FIG. 1, there is shown a perspective view of a preferred embodiment10, showing the front of the housing rack (“housing”) 100. Housing 100is preferably constructed of steel or another material suitable forproviding strength and stability. A preferred embodiment 10 has sixbattery modules (“modules”) 200 arranged vertically. When installed inhousing 100, each module 200 is secured in place by doors 110 with slamlatches 115. Slam latches 115 are attached to the front of each door110. The doors 110 prevent the modules 200 from sliding back and forthand preventing the contacts from becoming loose. Each door 110 extendsfrom the top of housing 100 to the exposed bottom sheath 202 of module200. Additionally, partitions 101 are fixed to housing 100 and locatedbetween each module 200 to prevent side to side movement. There are atotal of five partitions 101 fixed to housing 100. Each of the doors 110is hollowed out so that the display panels 225 on each module 200 arevisible. The display panels 225 are lit up using LEDs and indicate thestatus of each module 200. Further details regarding the display panels225 are shown in FIG. 15 and described later in the specification.

Representative Lift Truck

FIG. 2 shows a side view of a conventional Class I electric forklift130, which is representative of a prior art lift truck design with whichand in which the present invention may be incorporated, embodied orused. The particular model of forklift 130 illustrated is most like aCaterpillar model E6000 forklift, which specifies a 48V battery that is34.4 inches long (i.e., depth from front to rear)×39.5 inches wide(i.e., the lateral dimension when installed on the forklift)×23.3 inchesin height and that meets minimum weight requirements. As a Class Iforklift, forklift 130 is a mobile truck with a lifting assembly 131 forraising and lowering forks or other load supporting members 132 that areadapted to support a load 150 thereon, for the purpose of lifting,carrying or moving that load 150.

While the load supporting members 132 are conventionally designed tosupport the load 150 in a cantilevered fashion, extending forward of afulcrum generally created by the front wheels 142 of the forklift 130,heavier loads present risks of tipping over the forklift 130. Hence,minimizing that risk of tipping under load is basic to safe operation ofsuch a forklift 130 and, in line with its classification as a Class Ilift truck, the full range of weight (F_(L), illustrated by arrow 151)of the loads 150 to be carried by forklift 130 must be properlycounterbalanced by a counterweight force (F_(C), illustrated by arrow121). In other words, for safe lifting and maneuvering of a load 150without tipping, the forward-tipping torque created principally by theweight (F_(L), illustrated by arrow 151) of that load 150 must beexceeded by the opposing torque created principally by the counterweightforce (F_(C)) of the forklift 130, particularly for loads at the heavierend of the range of manufacturer specified load capacities for forklift130.

In the prior art, such a forklift 130 generally includes a large leadacid battery 160 as a major part of the counterweight force (F_(C)), andClass I forklifts are generally designed accordingly. The design of suchforklifts generally incorporates structure to safely support the weightof the forklift battery 160 within a battery compartment 122 of aparticular length (i.e., depth), width and height. The batterycompartment 122 is generally defined in part by removable or openablepanels or the like that partially or completely contain and define thespace for the forklift battery 160 therein. In the case of theillustrated forklift 130, for instance, the battery compartment 122 isdefined in part by a seat assembly 135 and a partial side panel 136. Theseat assembly 135 normally sits over the top of the forklift battery 160but has a releasable latch that allows it to be manually pivoted up andaway from the forklift battery 160 to enable an operator to access theforklift battery 160 or its compartment 122. Analogously, panel 136 orother structures are provided to help enclose and define the batterycompartment 122, and panel 136 may also be either removable or openableto enable more complete access to that battery compartment 122, such asfor purposes of checking or replacing the forklift battery 160 therein.Forklift 130 also has positive and negative electrical conductors forremovably connecting the forklift's electrical circuitry to thecorresponding terminals of the conventional forklift battery 160.

The forklift uses a fulcrum (illustrated by arrow 91) which is createdbetween the forklift's front wheels and the underlying floor 90. If themoment created by the load force (F_(L)) of load 150 forward of thatfulcrum 91 exceeds the opposite moment of the forklift counterweight(F_(C)), the forklift 130 will tip forward, toward the load 150,resulting in a dangerous situation. The location of the center ofgravity 161 depends partly on if the forklift is loaded or unloaded.When the forks 171 are raised while carrying a load 150, the center ofgravity 161 naturally shifts toward the front of the forklift andupward.

Rechargeable Lithium-Ion Battery Assembly

FIG. 3 shows the same representative Class I electric forklift 130 asillustrated in FIG. 2, but having a preferred rechargeable batteryassembly 230 according to the teachings of the present inventionoperatively installed in the battery compartment 122, in place of theconventional lead acid forklift battery 160 of FIG. 1. In contrast tothe conventional lead-acid battery 160, rechargeable assembly 230includes a plurality of separable battery modules 200, preferably aneven number of such modules 200 (six in the illustrated embodiment),each of which includes numerous lightweight lithium-ion battery cellstherein. Most preferably, those numerous battery cells are of the LFPtype. Even without recharging or replacing individual modules 200, theentire assembly 230 can hold an operable charge for around ten hoursbefore requiring approximately 60 minutes to recharge, in contrast tothe shorter usage durations and much longer charging durations that arecharacteristic of conventional lead acid battery 160. Also, due to theirlithium-ion chemistry, each module 200 can be cycled through about sixtimes as many charging cycles as conventional lead-acid battery 160.

For LFP chemistries in particular, charge rates corresponding to onehour or less charge times are often within the recommended operatinglimits of the cell. Additionally, the ease of removal of modules 200allows for opportunity charging during work breaks. For example, anoperator can remove a module 200 during a 15 minute break and get asubstantial recharge during this short interval. The longer run times ofrechargeable assembly 230 compared to conventional lead-acid batteries160 also improves workplace efficiency. For lead-acid batteries 160,large areas are allocated for recharging. After an 8-hour work shiftends, lead-acid battery 160 is removed for recharging and anothercharged lead-acid battery 160 is inserted. Replacing this system withrechargeable assembly 230 can save time and valuable space in the workenvironment.

Another important advantage of rechargeable assembly 230 is the lowerequivalent series resistance (ESR) in LFP batteries than lead-acidbatteries 160. Lead-acid batteries 160 experience decreased performanceas a result of having higher ESR. Often as these batteries 160discharge, a “voltage droop” occurs, causing sluggish operation of theforklift truck under load or acceleration. Most often, this occursaround 6 hours into a shift, requiring an additional recharge per shift,whereby reducing the life of the battery. LFP batteries provide animprovement in sustained performance during shifts while significantlyreducing the risk of voltage droop.

The preferred embodiment of rechargeable assembly 230 has six batterymodules 200 installed in a larger housing rack 100. Those modules 200are preferably arranged in two symmetrical groupings, half beingremovable from one lateral side of the housing rack 100, and the otherhalf being removable from the other lateral side of that housing rack100. The complete assembly 230 preferably contains two sets of sixmodules 200 arranged back-to-back and vertically oriented, the frontfaces of which are exposed on one side or the other of the forklift whenany detachable panels 136 are removed or opened. Alternative embodimentsmay have a different location or different quantities of battery modulesmaking up the housing rack 100.

Sized, weighted and otherwise adapted to be roughly comparable to theconventional battery 160, the height “H”, depth “D” and width (thedimension perpendicular to FIG. 2) of assembly 230 are substantially thesame as those for the conventional forklift battery 160 intended for usewith forklift 130. Hence, assembly 230 may be described as“forklift-battery-sized”. Due to its forklift-battery-sizedcharacteristic, for the forklift 130 as illustrated, assembly 230 isable to safely fit in the same battery compartment 122 as conventionalbattery 160. The preferred embodiment of rechargeable battery assembly230 is also weighted with centrally-oriented steel plates in its base,integrally secured to its lower surface 304, to meet the minimum (andmaximum) weight requirements of batteries to be used in forklift 130, asspecified by the manufacturer of forklift 130.

Hence, for use on the Class I electric forklift 130 shown in FIG. 3,lithium-ion battery assembly 230 is adapted to fit in a CaterpillarE6000 forklift battery compartment 122, for use as a replacement ofconventional lead-acid battery 160. More specifically, for the E6000,lithium-ion battery assembly 230 roughly fits the dimensions of 34.4inches long (i.e., depth from front to rear)×39.5 inches wide (i.e., thelateral dimension when installed on the forklift 130)×23.3 inches inheight, and assembly 230 has a minimum weight of 3100 pounds, preferablywith a margin of fifty pounds over the manufacturer's specified minimumbattery weight requirement.

Those of skill in the art will understand that the dimensions, fit,shape and weight for different makes and models of forklifts willdictate a range of dimensions for alternative embodiments that areintended to be used with any particular make and model of forklift. Thefull range of sizes for Class I forklift batteries are intended foralternative embodiments. The range of minimum battery weightrequirements for Class I electric forklifts are approximately 1,500 to4,000 lbs., which is also intended for alternative embodiments.

It is contemplated that the preferred embodiment allows for the removalof four modules 200 on each housing rack 100 for replacement orrecharge, while still being able to maintain operation of the forkliftwith two modules per rack 100. To accommodate continued operationdespite removal of one module 200, such removal will not decrease thevoltage below the requirement for the forklift 130.

Although many aspects of the present invention can be appreciated withother types of rechargeable batteries, preferred embodiments use batterycells of one of the lithium-ion types. Most preferably, each module 200of the battery assembly 230 incorporates hundreds of self-containedbattery cells of the LFP (lithium iron phosphate) type. Although alllithium-ion battery types can experience thermal runaway, LFP batterycells of the preferred embodiment have a fairly high thermal runawaytemperature, of 270 C, substantially higher than the runaway temperaturefor NCA or other LCO cells, which are the more conventional oflithium-ion battery cells, which typically have a thermal runawaytemperature of around 150° C. Although the preferred embodiment uses LFPbatteries, it should be understood that some aspects of the inventioncan be appreciated through use of other types of rechargeablelithium-ion battery cells. For example, alternative compounds for someaspects of the invention are contemplated to include, withoutlimitation, lithium cobalt oxide (LiCoO₂), lithium manganese oxide(LiMn₂O₄, Li₂MnO₃), lithium nickel cobalt aluminum oxide (LiNiCoAlO₂),and lithium nickel manganese cobalt oxide (LiNiMnCoO₂).

Within each of the battery modules 200 of the preferred embodiment, aplurality of self-contained battery cells (preferably somewhere in therange from one-hundred, sixty to two-hundred cells per module 200) isconnected in a combination of series and parallel using a wire bondingmethod. The wire bonding method connects batteries using wire bondsinstead of busbars. The wire bonding is achieved through ultrasonicfriction welding. By interconnecting batteries with wire bonding, thewire bonds can prevent short circuits while acting as fuses. The wirebonds are made of wire that allows for the expected current to passthrough without significant overheating and allows the wire bond tobreak to prevent over-currents of individual cells. Additionally, FET'sor other forms of conventional fuses are placed inside battery modules.If the current carrying capacity is exceeded, the fuse will open andprevent the overcurrent from also blowing out the wire bonds.Alternative embodiments of this design may connect battery cells inparallel. Additionally, alternative methods of connecting batteriescould include traditional soldering and spot welding.

Removal and Insertion of Battery Modules

Turning to FIG. 4A, there is shown a disengagement of a slam latch 115from the housing 100. The bottom end 116 of latch 115 is pushed down inorder to release the top end 117 from the engagement with housing 100.Pin 201 is permanently attached to door 110 and fits into the groove112. In FIG. 4B, there is shown a hinge 111 of door 110 that engagesmodule 200. Though not visible in FIG. 4B, door 110 has an identical pin201 on its opposite side. Similarly, module 200 has an identical groove112 on its opposite side. Pins 201 remain at the top of grooves 112until the door 110 is opened.

Turning to FIG. 5A, there is shown a door 110 of housing 100 in ahalfway open position. It is shown in FIG. 5A that module 200 isprotruding from the front edge 102 of housing 100. In FIG. 5B, the pin113 is shown halfway up the groove 112. When the door 110 is opened, it110 rotates counterclockwise on hinge 111. Simultaneously, pin 113 movesdown groove 112 toward the bottom of module 200. It should be understoodthat the same mechanism occurs at the same time on the opposite side ofmodule 200. As the door 110 is opened, the module 200 begins to slideout of the housing 100.

Turning to FIG. 6A, there is shown a door 110 of housing 100 in a fullyopen position, rotated 90 degrees from the closed position. As a resultof opening door 110, module 200 is pulled out of housing 100 andprotrudes from the edge 102. The carry handle 205 of module 200 isclearly visible in FIG. 6A. Carry handle 205 is preferably bolted tomodule 200 and can be detached. In FIG. 6B, the pin 113 is shown at thebottom of groove 112, enabling module 200 to be removed from housing100.

Turning to FIG. 7A, there is shown module 200 removed from housing 100and resting on door 110. At the top of module 200, there is a protectivetop sheath 203 with a hollowed out area for viewing display panel 225.Once the door 110 is in the fully open position, a user can manuallyslide module 200 along tracks (not shown) out of housing 100 and ontodoor 110. The preferred embodiment 10 has low friction slides locatedbelow each module 200. Turning to FIG. 7B, the user can manually foldthe carry handle 205 upward and lift module 200 off of the door 110. Theuser can carry module 200 using carry handle 205 to a battery chargingstation and replace it with another charged module 200. Preferably, thebattery modules 200 weigh no more than 51 pounds in compliance with OSHAand other workplace standards. Replacing a module 200 requiresperforming the opposite actions of the aforementioned removal procedure.

FIGS. 8A-11B show the procedure for removal of module 200 in analternative embodiment. Turning to FIG. 8A, there is shown adisengagement of a slam latch 115 from the housing 100. The bottom end116 of latch 115 is pushed down in order to release the top end 117 fromthe engagement with housing 100. In FIG. 8B, there is shown a hinge 111′of door 110′ that engages module 200. A pin 201′ that is permanentlyattached to module 200 fits into the groove 112′ in hinge 111′. The pin201′ remains at the bottom of hinge 111′ until the door 110′ is opened.

Turning to FIG. 9A, there is shown a door 110′ of housing 100 in ahalfway open position. In FIG. 9B, the pin 201′ is shown halfway up thegroove 112′. When the door 110′ is opened, the hinge 111′ rotatescounterclockwise around the fixed pin 201′. As the door 110′ is opened,the module 200 begins to slide out of the housing 100. At this time, anelectric switch (not shown) is actuated. The interlock pin 911 (shownschematically in FIG. 19) loops through the physical latch (not shown)in the slot where module 200 c connects. When module 200 c is insertedand the latch closes, the interlock pin 911 is shorted with moduleground pin 914. It is shown in FIG. 9B that module 200 is protrudingfrom the front edge 102 of housing 100. Turning to FIG. 10A, there isshown a door 110′ of housing 100 in a fully open position. As a resultof opening door 110′, module 200 is pulled out of housing 100 andprotrudes from the edge 102. The carry handle 205 of module 200 isclearly visible in FIG. 10A. Carry handle 205 is preferably bolted tomodule 200 and can be detached. In FIG. 10B, the hinge 111′ is shownrotated 90 degrees counterclockwise from the closed position. The pin201′ is outside groove 112′, enabling module 200 to be removed fromhousing 100. Turning to FIG. 11A, there is shown module 200 removed fromhousing 100 and resting on door 110′. Once the door 110′ is in the fullyopen position, a user can manually slide module 200 along tracks (notshown) out of housing 100 and onto door 110′. The embodiment has lowfriction slides located below each module 200. Turning to FIG. 11B, theuser can manually fold the carry handle 205 upward and lift module 200off of the door 110′. The user can carry module 200 using carry handle205 to a charging station and replace it with another charged module200. Replacing a module 200 requires performing the opposite actions ofthe aforementioned removal procedure.

Turning to FIG. 12, there is shown a rear view of housing 100. There aresix sets of fans 120 for cooling the modules 200. Each set has threefans 120 and the sets are located between modules 200. For example, thefirst set shown on the left of FIG. 12 is located between the first andsecond modules 200. The second set is located between the second andthird modules 200, the third set between the third and fourth modules200, the fourth set between the fourth and fifth modules 200, and thefifth set between the fifth and sixth modules 200. The sixth set of fansis located between the sixth module 200 and the housing 100 wall.Different numbers of fans are also contemplated by the inventor for thepurpose of providing module cooling. Six sections of the housing 100 arehollowed out so that the rear side connections of modules 200 areexposed. At the rear of each module, the 10-pin signal connector 210 andpositive 211 and negative 212 connectors are visible.

Turning to FIG. 13, there is shown a perspective view of a preferredembodiment 10, showing the back of housing 100. From this view, it isclearly shown that the positive 211 and negative 212 battery terminalsprotrude from the back surface 103 of housing 100. It is important tounderstand the purpose of having these connections 211, 212 protrudewhile signal connector 210 is recessed. It is necessary to make sure thehigh current battery terminals 211, 212 are mated before the batterymodule 200 is “enabled” during the insertion process. “Enablement”occurs when the 10-pin signal connector 210 goes through a series ofinterlocks with the bus (not shown). If the module 200 is “enabled”before it is physically connected to the bus and the bus voltage andbattery voltage differ, then at the moment the terminals 211, 212 mate,there will be instantaneous high current to equalize the potentials. Thepurpose of the mechanism is to ensure the high current connector ismated before enabling the battery module 200 and disabling the batterymodule 200 before it is disconnected for safety, notably to preventarcing which can damage electrical connectors.

For these reasons, the signal connector 210 is the last connector tomate during module 200 insertion and the first connector to disengageduring module 200 removal. This method requires the pins in the 10-pinconnector 210 to be substantially shorter than the battery terminals211, 212, so that during the removal process, the 10-pin connector willdisconnect while the battery terminals 211, 212 are still connected. Atthis point in the process, the module 200 will detect that it is nolonger connected to housing 100 via the 10-pin connector 210, and shutitself off instantaneously before the battery terminals 211, 212 aredisconnected.

Turning to FIG. 14, there is shown a rear view of battery module 200.The protective case 204 of battery module 200 is preferably constructedof aluminum or another lightweight material with similar properties. Thebottom sheath 202′ is hollowed out for the 10-pin connector 210 andbattery terminals 211, 212. Each module 200 has a microcontroller and isable to connect to a CAN bus using its 10-pin connector 210.

Turning to FIG. 15, there is shown a sectional front view of batterymodule 200. The top sheath 203 is hollowed out for the display panel 225and the carry handle 205. Display panel 225 is illuminated using LEDsand has a button 221 with a status bar 222 and a fault bar 223. A usercan press button 221 to “wake” the display from sleep mode. A coded pushcan be used for diagnostics. If the status bar 222 lights up blue, themodule 200 is operating normally. If the fault bar 223 lights up red,there is a fault with module 200. There are five bars 223 that light upgreen and indicate the battery charge level of module 200. The five bars223 will show charge status in increments of 20% of charge ranging from0%, to 100% based on the number of LEDs illuminated. For example, onebar indicates that the charge is very low (around 20%) and five barsindicates the module 200 is fully charged (100%).

Electrical Design of Battery Cell Network and Battery Module

Turning to FIG. 16, there is shown a perspective view of the interior ofmodule 200. Each battery cell 1710 is wire bonded to a printed circuitboard (PCB) 1722. Located between the battery cells 1710 and the PCB1722 is a top plastic battery tray 1720 a and a thermally conductiveglue 1721 or other adhesive Plastic battery trays 1720 a, 1720 b areplaced directly on top of and below the battery cells 1710. Thethermally conductive glue 1721 is used between battery trays 1720 a,1720 b and the PCB 1722. The thermally conductive glue 1721 is also anelectrical insulator.

Turning to FIG. 17, there is shown a top interior view of module 200.Each battery cell 1710 is wire bonded to a printed circuit board (PCB)1722. There are three wires 1725 a, 1725 b, 1725 c bonded to pads on thePCB 1722 for each battery cell 1710. Two of the wires 1725 a, 1725 b arenegative and one of the wires 1725 c is positive. The purpose of twonegative wires is for redundancy. The preferred embodiment contains 184LFP battery cells. The battery cells 1710 can be divided into groups of23 cells called “banks.” The BSS can monitor voltage, temperature, andstate of charge for banks but cannot monitor individual battery cells1710. Alternate embodiments may contain variations of the arrangement ornumbers of battery cells 1710.

Turning to FIG. 18, there is shown a cross sectional view of a singlebattery cell 1710. As previously mentioned, the battery cells 1710 andother components are surrounded by a protective enclosure 204,preferably constructed of aluminum. Directly above battery cell 1710,there is a plastic battery tray 1720 a. The thermally conductiveadhesive 1721 a is used between the top of battery cell 1710 and topbattery tray 1720 a. Similarly, the same thermally conductive adhesive1721 b is applied between the top battery tray 1720 a and the PCB 1722.It is clearly shown that positive wire 1725 c and two negative wires1725 a, 1725 b are wire bonded to the top of PCB 1722. Turning to thebottom of FIG. 18, the thermally conductive adhesive 1721 c is appliedbetween the bottom of battery cell 1710 and bottom battery tray 1720 b.Furthermore, a thermally gap filling material 1726 is used between thebottom of battery cell 1710 and the bottom of protective enclosure 204.The gap filling material 1726 allows heat to be transferred from thebattery cells to the enclosure 204 so it can dissipate from the module200.

Turning back to FIG. 17, each module 200 has an integrated batterysupervisor system (BSS). The BSS 1700 monitors the health to includecell voltage, current, and temperature. Each module 200 is composed of aplurality of battery cells 1710 connected in series and parallel viawire bonding and ultimately terminating into an integrated BSS 1700. Thewire bonding will be completed using a method similar to the Teslaultrasonic friction welding method. The holes shown are used to wirebond the battery cells 1710 to the PCB 1722. In each hole, tiny wires1725 a, 1725 b, 1725 c will be bonded to both the PCB 1722 and thebattery cell 1710. The PCB 1722 is then used to directly transfer theelectric current through the interior of the battery module 200. The useof the PCB 1722 prevents the entire battery module 200 from failing ifone battery cell 1710 malfunctions because the other cells are stillconnected to the plate.

200200 The preferred embodiment of the BSS 1700 uses real-time batterycell information and compares this information to a set of referencevalues. It uses this comparison to determine abnormalities in individualbattery cells and in the plurality of cells to diagnose the problem. Thediagnostic information can be transmitted externally using acommunication unit. The BSS 1700 will also use this real-time data toprevent any issues during the battery operation by disconnecting thebattery from the housing rack 100 electronically if it senses a problem.

During charging, the BSS 1700 monitors the depth of discharge for eachbank of 23 cells, compensates for voltage temperature differences, andensures battery banks are properly balanced. If one battery cell hasslightly more or slightly less capacity than the rest of the batteries,then its level of discharge will deviate from the other batteries overseveral charge and discharge cycles. The BSS 1700 must balance thebatteries to prevent over-discharge as well as over-charge, which causesdamage and eventually complete battery module failure and can present asafety risk.

Charge Management Systems Integration

FIG. 19 is a schematic diagram where the six battery modules 200 a-f areconnected in parallel to the housing rack 100. At any particular pointin time, each battery module 200 may have a different state of charge,particularly as the module charges are drained through use in poweringthe forklift. The “state of charge” is defined as the percentage chargethe module 200 currently has. Each module 200 may be at a differentinitial voltage due to differences in battery life or initial chargelevels. Each module 200 may also have a different max voltage when theyare “fully charged,” considering differences in age and usage ofparticular modules 200. For example, module 200 a may have a voltage of24.0 V when fully charged while module 200 f may have a voltage of 23.9V when fully charged.

It is necessary for a Battery Operating System Supervisor (BOSS) moduleprocessor (“BOSS module”) 901 to serve as a battery management systemfor the modules 200 a-f. But for the control of BOSS module 901, in suchscenarios where the voltage in one module exceeds the others, the lowervoltage battery modules would draw a current flow from the highervoltage modules into the lower voltage modules that would be onlylimited by resistance of the connectors, cells, bus bars, and bondwires. A large difference in voltage would cause high current flow tothe battery module with lower voltage. These situations are undesirablebecause the current flow to the motor is reduced as current flowsbetween battery modules, rather than out of the housing 100. If a highcurrent is maintained for an extended period of time, or the voltagediscrepancy is high enough such as to produce a current higher than thehandling capability of the bond wires, it can also lead to batteryfailure by draining the battery rapidly or opening the bond wires.

Turning back to FIG. 19, there are a total of three bus bars which themodules 200 connect to. The negative terminals 212 of the modules 200will either connect to the 0 V (ground) bus bar or the 24 V bus bar,depending on the grouping. Half of the modules 200 negative terminals212 will connect to the 0 V bus bar and the other half will connect tothe 24 V bus bar. The positive terminals 211 of the modules 200 willconnect to the 48 V bus bar. As previously described, the Boss module901 grants permissions to battery modules 200 to determine which areconnected to the bus bars and which modules 200 are disconnected, bysending signals to the modules 200. Modules 200 then use MOSFET switchesto connect and disconnect.

It should be understood that module 200 c is used here only as anexample and that each module 200 is wired and employed in the samemanner. Communication between the BOSS module 901 and the modules 200 isbest understood by describing the low voltage ten-pin connection 210,(actual connector 210 shown in FIG. 14) depicted schematically in FIG.19. Four of the pins are “isolated” and five pins are “non-isolated,”with one spare pin not currently utilized but may be employed later. Theterm “pin” is also used here when describing the wires corresponding totheir respective pins in wire harnesses 904 and 909. The isolated pinsare grouped as part of an isolated wire harness 904. It will beunderstood by those of ordinary skill in the art that “isolated” refersto galvanic isolation. Transformers are used to separate the isolatedwire harness 904 from the main power supply. If an electrical shortoccurs in the isolated wire harness 904, there is no risk of damage tothe rest of the circuits in the system. The isolated wire harness 904 isdepicted as the upper dashed line connected to module 200 c. Isolatedwire harness 904 also connects to the vehicle bus 920. The vehicle bus920 is the communication network depicted by the multiple dashed lines.When a module 200 c is inserted into a “slot” in housing 100, theisolated 5 V pin 905 connects to it and signals the BOSS module 901.There are two pins 905, 906 for communication between module 200 c andBOSS module 901. There is a CAN HI pin 906 and a CAN LO pin 907. Lastly,there is a ground 908 pin on isolated wire harness 904.

The non-isolated pins are grouped as part of a non-isolated wire harness909. When module 200 c is inserted in housing 100, the identification(ID) pin 910 connects to the BOSS module 901 in order to assign CANaddresses in the housing 100 (identify the slot position of the module200 c within housing 100). The interlock pin 911 loops through thephysical latch (not shown) in the slot where module 200 c connects sothat the BOSS module knows that module 200 c is connected. There is alsoa pin 912 for controlling fan power, a pin 913 for controlling fanspeed, and a module ground pin 914. Battery module 200 c (and allbattery modules) is responsible for controlling its own fan speed andfan power. When module 200 c is inserted and the latch closes, theinterlock pin 911 is shorted with module ground pin 914. Once thisoccurs, the BOSS module 901 can then grant permissions to module 200 cto connect to the bus bars.

An example of the importance of BOSS module 901 can be understood duringcontinuous operation of a forklift and replacement of modules 200. Whilethe forklift is operating, the process of inserting a fully chargedmodule 200 is known as “hot swapping.” Looking at FIG. 19, module 200 cis fully charged and was inserted while modules 200 a-200 f were alreadyconnected. BOSS module 901 will not grant permission for module 200 c toimmediately connect to the bus bars. Module 200 c will wait until thereis a low demand on the other modules 200 before connecting to the busbars. Low demand refers to a time when the forklift does not require alot of current. For example, a forklift carrying a load and driving up ahill would require a lot of current. When the forklift is idle, thecurrent demanded will be low and this would be an appropriate time formodule 200 c to connect. The BOSS module 901 does not control thedisconnection and connection of modules 200 from the bus bars. BOSSmodule 901 only grants permissions to the modules 200 for the conditionswhen they are able to connect and disconnect. Each module 200 usesinternal MOSFET switches 903 a-f to rapidly open and close the circuitconnections from the modules 200 to the bus bars. Once a fully chargedmodule 200 c is connected, a module 200 at a lower state of charge candisconnect. For example, if module 200 f is at 60% and the other modules200 are above 80%, module 200 f will disconnect and only reconnect oncethe other states of charge decrease to about 60%. 200.

For at least these reasons, BOSS module 901 in housing 100, to theextent networked, is designed to monitor the states of charge in eachmodule 200 and will grant permission for a module 200 that varies bymore than some threshold to disconnect. This allows the forklift tocontinue operating without hindering to performance. The specific 24 Vbattery modules are used in preferred embodiments, but alternativeembodiments can use various voltages depending on the needs of theparticular lift truck.

200 Another important feature of the system can be described in a casewhen there is an empty housing and the system is completely turned off.When the modules 200 are unplugged from housing rack 100, theyautomatically turn off. With an empty housing 100, when module 200 a isinserted, the BOSS module 901 will not power on by itself. For thisreason, preferred embodiment 10 has a continuously hot separate 5 Vcontrol connector 905. When module 200 a is inserted, it connects tocontrol connector 905 which powers up the BOSS module 901. This processoccurs on a 5 V bus, separate from the vehicle bus 920. Since thecurrent is so low on the 5 V bus, there is no risk of arcing. 200Although the aforementioned figures depict a housing rack 100 with oneside, preferred embodiments will be two sided with six modules 200 oneach side for a total of 12 modules 200. In the preferred embodiment,six battery modules 200 are connected in parallel in each housing 100 toattain a higher current capacity at a constant voltage. Alternativeembodiments may employ any number of battery modules.

Alternative Embodiments

The following sections describe alternative embodiments of the disclosedsystem.

Lithium-Ion Battery Module System Design

FIG. 21 provides an elevation view of the rechargeable battery assembly220 of the alternative embodiment, separate from forklift 130. Therechargeable battery assembly 220 has eight removable andinterchangeable battery modules 330 a-330 h, which are operativelyinserted in one of the eight identical module bays 301 a-301 h definedwithin an outer housing 300. The housing 300 makes up the outer surfacesof the larger battery assembly 220, and the overall height (“H”, aslabeled in FIG. 21), depth (“D”, as also labeled in FIG. 3) and width(i.e., the dimension perpendicular to the sheet of FIG. 3; width notbeing labeled in FIG. 21) of the assembly 220 is about the same as theheight, width and depth of lead acid batteries 160 (shown in FIG. 2)that are of a size suitable for intended use in forklift 130.

The alternative embodiment has the form of a unitary housing rack 300with a capacity of receiving and managing eight removable batterymodules 330, each of which is interchangeable with the others. FIG. 21only shows four modules because the alternative embodiment has twosymmetrical arrangements of four modules aligned back-to-back. This isso that the handles are exposed to the openings of the detachable panelon the forklift 136 on both sides. This also simplifies the connectionpoint in the housing rack to only one location. The housing rack 300 ofserves multiple purposes and benefits. In addition to housing thebattery modules 330 within the forklift 100, the rack can be removed,and used as a charging station, typically a floor-standing chargingstation. The housing rack 300 in the alternative embodiment isconstructed of a metal. Particularly in preferred embodiments, housingrack 300 will be constructed of steel which provides durability. Inaddition to providing durability, having housing rack 300 constructed ofsteel adds weight that helps to prevent housing rack 300 from tippingwhen one or more battery modules 330 are removed, particularly whenhousing rack 300 is used as a charging station. Other materials arecontemplated including, but not limited to, composites and polymers.

In addition to having dimensions that are forklift-battery-sized, aspreviously explained, the lowermost surface 304 of housing rack 300 ispreferably weighted by the addition of a heavyweight material affixedthereto, preferably in the form of steel plates resting thereon butwithin the enclosure of housing 300. The added weight of those steelplates increases the weight of the overall assembly 220, so that itweighs more than the minimum battery weight specified by themanufacturer of forklift 130, while still enabling the lightweightcharacteristic of removable modules 330, which each weigh less thanfifty-one pounds. It will be evident to those skilled in the art thatthis counterweight will consist of a heavyweight material, such as ahigh-density steel, and may be composed of multiple plates or sectionsto allow the user to manipulate the center of gravity 161 to maximizethe safe lifting capabilities of the forklift. Alternate embodiments mayinclude, but are not limited to, different locations of an adjustablecounterweight, such as on top of the housing rack, or the multiplevariations of the material of the housing rack and counterweight. Thehousing rack 300 may be designed in such a manner so that the rackitself can be replaced by a housing rack 220 of different material toadjust the counterweight.

It is contemplated that the minimum battery weight requirements will besatisfied by a housing rack 300 and counterweight with less than acomplete arrangement of battery modules 330. This is to allow for theuser to still safely operate the forklift 100 in the event that thereare not enough battery modules with enough charge. Alternativeembodiments will be able to meet weight requirements with 6-7 modules.Other alternative embodiments will ideally meet minimum weightrequirements with somewhere between 1 and 3 batteries 330 short of acomplete arrangement.

Combined with the moderate weight of the housing rack 300, alternativeembodiments weigh substantially less than a conventional lead-acidbattery. Even in situations where the housing rack 300 has an incompletearrangement of battery modules 330, the modules will still weigh lessthan 51 pounds. Each battery module 330 or “pack” is equipped a handle335, at the rear of the module. The handle 335 will be designed toensure easy gripping and for safe movement of the module. The design ofthe handle and functional method for removal and installation of themodules 330 will be discussed in more detail in subsequent sections.

Alternative embodiments include other adaptations to enable and ensuresafe removal of both the battery modules and the housing rack 300 fromthe forklift 130. Preferably, there is a module release button 333 onthe back of each battery module 330 that will ensure safe disengagementof the module 330 from the housing rack 300, safe release beingconsidered from a mechanical perspective. Electrical disengagement willoccur with an interlock pin configuration. This button will be describedin more detail in the following section, “Housing Rack and BatteryModule Interface Design.” The front of the battery module will also havean indicator that will show if the battery is actively engaged or hasbeen switched off. It will be evident to those skilled in the art thatthis indicator may take on a variety of alternate embodiments including,but not limited to, a small led indicator, a light that illuminates as apart of the button 333, or a LCD display panel on the front of thebattery pack that also displays other indicators about the health of thebattery. In this alternative embodiment, the LCD display panel willdisplay indicators used to monitor battery health including but notlimited to voltage, temperature, and remaining battery usage time.

FIG. 21 includes another important safety feature. There is an eyehook226 located within a boss 225 at the top of the housing rack assembly300. The alternative embodiment of the housing rack 300 will includeeyehooks 226 at both ends of the housing rack for easy removal orinstallation of the rack into the forklift battery compartment. It willbe evident to those skilled in the art that the structure of this boss225 and eyehook 226 will mimic the existing eyehooks 125 and saferemoval mechanisms currently used in the design of the conventionallead-acid battery 160 to ensure complete backwards compatibility. Thismay differ in shape from the representation in FIG. 21. Alternateembodiments may utilize different methods for the removal of the housingrack 300 from the forklift 130, but will be utilized so that the removalis conducted in a safe and convenient manner.

FIG. 22 shows a rear view of one half of the housing rack 300, so thatthe battery pack connection points are visible. The location of thisviewing plane is shown as section 4-4 in FIG. 23. There is anothereyehook 226 at the top of the rear of the housing rack 300. Located atthe rear of the battery pack 330, the six-pin male connector 400 and thepositive 401 and negative 402 battery terminals are the only wiredconnection points for engaging and disengaging the module. Within eachmodule 330 is a plurality of lithium-ion battery cells. It will beunderstood by those of ordinary skill in the art that other connectorswith various numbers of pins may be implemented. The outer casing of thebattery module 330 is constructed of a hard, lightweight metal. Othermaterials are contemplated including, but not limited to, alloys,composites, and polymers.

FIG. 23 is an isometric view of the alternative embodiment of thehousing rack 300. The alternative embodiment will have eight (four shownhere) battery modules 330 arranged back-to-back in two stacks of four.When installed in housing 300, each module 330 sits on top of lowfriction slides 310 that allow for the smooth motion of the modules 330into and out of the corresponding bay 307 in the housing 300 forassembly. Also, the features previously described on the module areincluded in this view. The front of each module has a handle 335 and theback has a button 333 for removal. The button on the rack will releasethe unit to be pulled from the rack. The pack will rely on a pininterlock (first to connect, last to break) to turn power on/off to thehigh current terminals. The latch is meant to keep the battery in placeso that the contacts do not become loose. At the rear of each module the6-pin connector 400 and positive 401 and negative 402 connectors arevisible. Additionally, the eyehooks 226 and bosses 225 are visible atthe front and rear of the housing rack 300.

Battery Module Design

FIGS. 24A and 24B are isometric views of the battery module 330 showingthe individual battery module and the frictionless slide 310. FIG. 24Adepicts the front of the alternative embodiment of the module 330 withboth the disengagement button 333 and handle 335 visible. As previouslymentioned, the handle 335 will be used to safely carry and remove themodule 330. As clear from FIG. 24A, the alternative embodiment uses ahandle bolted on behind the face of the module 330. It will be evidentto those skilled in the art that the handle will be located to ensureeasy lifting and gripping and relative dimensions and location may varyfrom those shown in FIG. 24A. The handle 335 is designed to carry theweight of the entire module.

The handle 335 allows the user to move the module 330 in the housingrack 300 in a fashion similar to a drawer and is constructed of a hard,lightweight metal. Other materials are contemplated including, but notlimited to, alloys, composites, and polymers. Alternate embodiments arecontemplated that could include a handle at the rear or handles on theside of the individual modules 330. Each of these handles will befashioned in a manner to the battery module 330 to allow for the easygripping and for safe movement of the module. It will be evident tothose skilled in the art that handles added to module of the alternativeembodiment may have hinges to lie flat with the surface, so that theywill not interfere with the battery connection points or movement in andout of the battery rack 300.

FIG. 24B depicts the rear of the battery module. The six-pin connector400 is wired directly to a BSS that is used to monitor battery health.Finally, the positive 401 and negative 402 terminals are connected tothe same plurality of battery cells. The positive 401 and negative 402terminals connect to the housing rack 300 through the use of a quickrelease connection. The requirements for this quick release connectionare that they are able to: maintain performance through a high number ofcycles, blindly connect the battery module 330 and the housing rack 300,and safely transfer current from the module 330 to the housing rack 300through multiple contact points. The alternative embodiment makes use ofa spring biased connection that that allows each battery terminal 401and 402 to slide into the corresponding socket when the battery module330 is connected. Other alternative embodiments may make use of asimilar quick connections that allow for blind sliding connecting anddisconnecting.

Due to the nature of utilizing multiple battery modules 330 in a largerhousing rack 300, the removal and installation of modules into the rackis an important aspect of this design. The alternative embodiment haslow friction slides 310 located below each battery pack. Alternativeembodiments may use other methods to achieve this sliding motion toposition the modules 330 in the housing rack 300, such as the use ofrollers or ball bearings to facilitate removal and installation.

In such an alternative embodiment, the module 330 slides on cylindricalrollers with roller bearings and is guided by a track on each side ofthe module, in the same location as the frictionless slide 310. Therollers and roller bearings would be constructed of lightweight metal inthe embodiment. Alternative embodiments may employ various types ofroller bearings and rollers constructed of different materials besidesmetal. It is contemplated that every embodiment of the design willinclude some method to prevent the module from moving uncontrollably outof the assembly.

It is contemplated that the alternative embodiment of battery moduleremoval will accomplish two things: have a mechanism to prevent thebattery from being removed in an uncontrolled manner, and not add anexcessive number of additional moving parts to the battery moduledesign. The alternative embodiment, in FIG. 24A, includes two stops 603and 604 located on either side of the module connected to the housingrack 300. There are also two tabs on either side of the module 605 and606. The stops 603 and 604 are meant to catch the battery tabs 603 and604 along the rear of the sides of the module to prevent the batteryfrom sliding out unexpectedly. The motion of the battery module 330during removal in the alternative embodiment is shown in the FIG. 24A asthe dashed section 607. The module 330 will be removed from the housingrack assembly 300 by gripping the handle 335 at the front of the moduleand sliding the case forward in the direction of arrow 608. The modulewill slide along the low friction slides 310, until the battery tabs 605and 606 come into contact with the stops 603 and 604 on the housing rackassembly 300. The module 330 must then be lifted over the stops 603 and604 to be completely removed in the direction of arrow 609. Theinstallation motion, in this alternative embodiment will require theexact reverse order of steps for removal.

Other alternative embodiments of this design may include, but are notlimited to, a stop that allows the battery module 330 to pivot androtate 90° downward so the battery can be lifted off a pivot rod by ahandle at the rear of the module. Furthermore, the pivot rod ispreferably connected to rotational dampeners positioned on either sideof housing rack 300. These rotational dampeners will slow the rotationof the battery module 330 to its vertical lift-out orientation duringremoval which decreases the chance of damage to the battery module 330or the housing rack 300. Alternate embodiments contemplated may includedetents or latches on the exterior of the battery, but they will beimplemented so as not to fail before the life of battery has ended.

Electrical Design of Battery Cell Network and Battery Module

FIGS. 25A and 25B show an isometric view of the top and bottom of thebattery module 330, respectively. Each battery pack 330 is composed of aplurality of battery cells connected in series and parallel via wirebonding to and ultimately terminating into an integrated BSS 700. Thewire bonding will be completed using a method similar to the Teslaultrasonic friction welding method. Although wire bonding has beenwidely used in other contexts such as with integrated circuits anddiscrete electronics, the battery industry has incorporated wire bondingthat allows for boding larger gauge wires than has previously been done.Both figures show a plurality of battery plates 701-709. The holes shownin each plate are used to wire bond the battery cells to the plates. Ineach hole a tiny wire will be bonded to both the plate and the batterycell. The plates are then used to directly the transfer the electriccurrent through the interior of the battery module 330. The use of theplates prevents the entire battery module 330 from failing if onebattery cell malfunctions because the other cells are still connected tothe plate.

The plurality of cells is connected by the arrangement of plates 701-709as shown in FIGS. 25A and 25B. There are four plates (702, 704, 706, and708) located at the top of the interior of the battery module and fiveplates (701, 703, 705, 707, and 709) located at the bottom of theinterior of the battery module.

Each plate alternates between positive battery cell arrangements andnegative battery cell arrangements. For plates 702-708, this is roughlyhalf of the geometric area of the space. In the alternative embodiment,each of these interior plates is in contact with 50 battery cells, withone half being a negative contact and the other half being a positivecontact, and the most negative and most positive plates are in contactwith 25 cells each. Plates 701 and 709 are only in contact with 25 cellsas they are only in contact with the positive (701) or negative (709)ends of the battery cells. These plates are also directly connected tothe battery terminals or the BSS. Plate 701 is connected to the BSS,which is then connected to the positive terminal 401. Plate 709 isconnected to the negative terminal 402. The alternative embodimentcontains 200 LFP battery cells. Alternate embodiments may containvariations of the arrangement or numbers of battery cells. This alsoimplies that the plates in alternate embodiments could have differentnumbers, arrangements, or geometry than the alternative embodiment.

The flow of current through the battery cells alternates between the topand bottom of the module 330 as it works its way around the module 330interior. The current flows from the positive terminal 401 to plate 701,located on the bottom of the battery module (FIG. 25B). Plate 701 ispositively charged and in contact with only the positive end of the 25battery cells above it. The negative ends of these battery cells are incontact with the negative portion of plate 702, located at the top ofthe battery module (FIG. 25A). The negative portion of plate 702 isshown by the dashed section 702 a. The other half of plate 702, 702 b,is in contact with the positive end of the 25 cells beneath it. Theplate has contact with 25 negative battery cell ends, in 702 a, and 25positive cell ends, in 702 b. Subsequently, the negative end of thebattery cells for plate 703 are the same cells that have a positiveconnection with the 702 b portion of plate 702. These cells have anegative connection to plate 703. The other half of plate 703 lies inthe region of 704 a. This region contains the positive contacts with thebattery cells. Region 704 b of plate 704 continues the pattern and has anegative connection to plate 705. The contacts here on plate 705 arenegative. The other half of plate 705 is positively connected and thecells also have a negative connection with plate 706 in region 706 a.The region 706 b is positively connected on the top and on the bottom,is negatively connected to plate 707. The other half of the plate ispositively connected and has a negative connection with 708 a. Thecurrent passes through the positive connections in 708 b. By the timethe current reaches the negative plate 709, and a negative voltage flowsfrom the negative terminal 402.

The integrated BSS 700 monitors the health of the module 330 includingcell voltage, current, and temperature. With respect to monitoring, insome embodiments, for purposes of monitoring the status of the batterymodules 330, a display having multiple LED lights may be incorporated.For instance, the display may have seven (7) LEDs wherein five (5) ofthe LEDs show charge status in increments of 20% of charge ranging from0% to 100%, based on the number of LEDs illuminated. The other two (2)LEDs may show status and trouble codes based on the color ofillumination and/or by a series or pattern of blinking of the LEDs,wherein different blinking series or patterns relate to particulartrouble codes. Furthermore, each display may incorporate a push buttonthat may be used to query the status of the particular battery module330, and also can be used to troubleshoot the battery module 330 by thenumber of presses of the button or by the duration of a button press.Each view (FIG. 25A-25B) shows a flex cable 710 wired along from the BSS700 and the six-pin connector 400 to each of the sections of batterycells. The flex cable 710 will be used to wire all diagnosticinstrumentation in the alternative embodiment to measure temperature,current, and voltage. Additionally, each module 330 will contain anarrangement of field-effect transistors (FETs) 711 in series with thebattery cells to ensure the proper power handling. These switches arethe aspect of the alternative embodiment that allow the module to beremoved from the housing rack 300, as well as function as an active andresettable fuse element. The number of FETs 711 is based on the powercapacity of the plurality of cells, and when removing the module 330from the housing rack 300, they disable the power to the terminals. Onealternative embodiment has twenty FETs 711, but other alternativeembodiments of this design with different power capacities willunderstandably have a different number of FETs or the equivalent.

An alternative embodiment of the BSS 700 uses real-time battery cellinformation and compares this information to a set of reference values.It uses this comparison to determine abnormalities in individual batterycells and in the plurality of cells to diagnose the problem. Thediagnostic information can be transmitted externally using acommunication unit. The BSS 700 will also use this real-time data toprevent any issues during the battery operation by disconnecting thebattery from the housing rack 300 electronically if it senses a problem.

During charging, the BSS 700 monitors the depth of discharge for eachcell, compensates for voltage temperature differences, and ensuresbattery cells are properly balanced. If one battery cell has slightlymore or slightly less capacity than the rest of the batteries, then itslevel of discharge will deviate from the other batteries over severalcharge and discharge cycles. The BSS 700 must balance the batteries toprevent over-discharge as well as over-charge deep discharge, whichcauses damage and eventually complete battery module failure and canpresent a safety risk.

The controller area network (CAN) communications protocol is used in thealternative embodiment as the main BSS. A CAN bus has error detectionand fault tolerance, but has some significant materials cost andcommunications overhead. For transmitting information, variouscommunication systems can be implemented. Other alternative embodimentscan use industrial transmission interfaces such as serial peripheralinterface (SPI), DC-BUS, or local interconnect networks (Lin Bus). TheCAN in the alternative embodiment would interface with each BSS and beable to effectively monitor and control the performance of the entirebattery housing rack. This prevents battery-to-battery performanceissues and uses each module as effectively as possible. This way, theCAN allows the housing rack to interact with the VCU as a single unitrather than allowing each battery module to interact individually withthe VCU. Furthermore, an isolated CAN scheme may be implemented thatallows for communication with the battery modules in the “top” of thestack of battery modules, wherein those battery modules may be sittingat a potential that is some voltage higher than those battery modulesthat are lower in the stack.

Housing Rack and Battery Module Interface Design

FIG. 26 is a top view schematic diagram of the battery module showingthe mechanism for removal and installation in the rack. The batterymodule 330 is removed by pressing a button 333 on the outside handle.The button 333 is meant to ensure that the module 330 remains in placeduring operation of the forklift. Pressing the button 333 releases thetension from the spring-loaded male connector 800, ejecting the maleconnector 800 from the female connector 801, and disconnecting thebattery module terminals 401 and 402 from the housing rack terminals 802and 803. The male connector 800 and the female connector 801 are thefirst to engage and the last to disengage. In FIGS. 26, 800-803, 401,and 402 are symbolic representations for illustration purposes. Thealternative embodiment of this portion of the system will be differentsizes and more intricate, but accomplish the same task.

To install a removable battery module 330 within a slot-like bay 307 ofthe rack 300, the user first manually positions its back face in theopening for the corresponding bay 307 and then manually slides itrearward into that bay. Once the module 330 slides far enough in so thatits back face contacts the spring loaded male connector 800, connector800 begins to compress. After the connector 800 is completelycompressed, the module 330 locks in place. It is contemplated that theconnector 800 will be constrained from moving along the axis ofinsertion. The system is spring loaded to achieve pressure contact forthe battery module terminals, 401 and 402, to the housing rackterminals, 802 and 803. The male connector 800 pushes a back switchwhich acts as the on/off mechanism for the system located within thefemale connector 801.

Additionally, there is a need to safely disengage the battery modulefrom the housing rack before removing it completely to prevent arcing.Arcing leads to overcurrent and can cause destruction of the battery inthe absence of proper safeguards. Particularly, if the battery module330 is enabled before it is physically connected to Particularly, if thebattery module 330 is enabled (i.e., electrically connected) to the maleconnector 800 before it is physically connected to the male connector800, and the voltage of each differs, then the moment the connectors 800and 801 physically mate, there will be instantaneous high current toequalize the potentials. The goal is to ensure the high currentconnector is mated before enabling the battery module 330 and disablingthe battery module 330 before it is disconnected. This can be achievedthrough a plurality of methods. One such method is to use the button 333next to the handle to send a signal to the processor to disconnect powerto the terminal. An alternative method uses a pressure-sensitive switchat the rear of the battery module and only when the battery is fullyengaged with the connector will the battery be switched on. The relativedimensions of the switch and the power connectors will be such that theswitch will protrude just far enough from the rear of the battery sothat it is disengaged before the battery module is completelydisconnected.

Another alternative method is through an electronic signal. Aspreviously mentioned, the battery module will connect to the housingrack with both a pin connector and battery terminals. The electronicsignaling method would require the pin connectors to be substantiallyshorter than the battery terminals, so that during the removal process,the pin connector will disconnect while the battery terminals are stillconnected. At this point, the battery module will detect that it is nolonger connected to housing rack via the pin connector, and shut itselfoff instantaneously before the battery terminals are disconnected. Itwill be understood by those of ordinary skill in the art that mechanismsother than those employed in FIG. 26, or described as alternatives, canbe employed in alternative embodiments. The purpose of the mechanism isfor safety, notably to prevent arcing.

An additional feature of an alternative embodiment is reflected in thebattery module 330 being compatible with prior art chargers used forrecharging the conventional battery assemblies 160 (shown in FIG. 2)with which forklift 130 is designed to be used. Due in part toApplicant's design of lithium iron phosphate cell modules 330 that canbe safely charged by conventional chargers when assembled in modulesaccording to the embodiments, the character and structure of the modules330 is such that the lithium-ion batteries are able to recharge withchargers currently used and already installed in warehouses thatrecharge conventional forklift batteries 160.

Charge Management Systems Integration

FIG. 26 is a schematic diagram an alternative embodiment where the eightbattery modules 330 a-330 h are connected in parallel to the housingrack 300, which has its own BSS 901. At any particular point in time,each battery module 330 may have a different voltage, as suggested bythe voltage numbers noted in FIG. 26, particularly as the module chargesare drained through use in powering forklift 130. Each module may be ata different initial voltage due to differences in battery life orinitial charge levels. In the example in FIG. 26, a couple of themodules have a fully charged voltage of 36.0 V, while others have lesservoltages as noted.

But for the control of BSS 901, in such scenarios where the voltage inone module exceeds the others, the lower voltage battery modules woulddraw a current flow from the higher voltage modules into the lowervoltage modules that would be only limited by resistance of theconnectors, cells, bus bars, and bond wires. A large difference involtage, will cause high current flow to the battery module with lowervoltage. These situations are undesirable because the current flow tothe motor is reduced as current flows between battery modules, ratherthan out of the housing rack. If a high current is maintained for anextended period of time, or the voltage discrepancy is high enough suchas to produce a current higher than the handling capability of the bondwires, it can also lead to battery failure by draining the batteryrapidly or opening the bond wires.

For these reasons, the main BSS 901 in the housing rack 300 to theextent networked, is designed to monitor the voltages in each module andwill disconnect a module that varies by more than a threshold of 0.10V.This allows the forklift to continue operating without hindering toperformance. Specific 36 V battery modules are used as an example asalternative embodiments can use various voltages depending on the needsof the particular lift truck.

Other alternative embodiments of battery monitoring system architectureare contemplated within the scope of the present invention. In oneembodiment, each battery module contains a PC board with a digitalisolator and a multi-cell battery stack monitor. Each module has anindependent interface connection to a controller board with amicrocontroller, a CAN interface, and a galvanic isolation transformer.The microcontroller is able to provide the gateway to the forklift'smain CAN bus and coordinate the modules.

In another alternative embodiment, each multi-cell battery stack monitor(MBSM) is on a PC board within each battery module. The BSS alsocontains a CAN transceiver and a galvanic isolation transformer. Eachmodule communicates through the MBSM non-isolated SPI-compatible serialinterface. This structure requires a 3- or 4-conductor cable connectedbetween battery modules. Only one microcontroller controls all thebattery monitors through the bottom monitor integrated circuit. Thismicrocontroller also serves as the gateway to the forklift's main CANbus.

Another contemplated embodiment has no monitoring and control circuitrywithin any of the battery modules. One PC board has 3 MBSM integratedcircuits (for 3 modules), each of which is connected to a batterymodule. The MBSM devices are able to communicate through non-isolatedSPI-compatible serial interfaces. One microcontroller controls all thebattery monitors through the SPI-compatible serial interface and is thegateway to the forklift's main CAN bus. Similar to the precedingdisclosed embodiments, a CAN transceiver and a galvanic isolationtransformer complete the BSS.

STILL OTHER ALTERNATIVES

Although the present invention has been described in terms of theforegoing disclosed embodiments, this description has been provided byway of explanation only, and is not intended to be construed as alimitation of the invention. For instance, despite reference to Class Iforklifts as such, it should be understood that some aspects of theinvention may have broader application with other types ofbattery-powered industrial trucks. Indeed, even though the foregoingdescriptions refer to numerous components and other embodiments that arepresently contemplated, those of ordinary skill in the art willrecognize many possible alternatives that have not been expresslyreferenced or even suggested here. While the foregoing writtendescriptions should enable one of ordinary skill in the pertinent artsto make and use what are presently considered the best modes of theinvention, those of ordinary skill will also understand and appreciatethe existence of numerous variations, combinations, and equivalents ofthe various aspects of the specific embodiments, methods, and examplesreferenced herein.

Hence the drawings and detailed descriptions herein should be consideredillustrative, not exhaustive. They do not limit the invention to theparticular forms and examples disclosed. To the contrary, the inventionincludes many further modifications, changes, rearrangements,substitutions, alternatives, design choices, and embodiments apparent tothose of ordinary skill in the art, without departing from the spiritand scope of this invention.

Accordingly, in all respects, it should be understood that the drawingsand detailed descriptions herein are to be regarded in an illustrativerather than a restrictive manner, and are not intended to limit theinvention to the particular forms and examples disclosed. In any case,all substantially equivalent systems, articles, and methods should beconsidered within the scope of the invention and, absent expressindication otherwise, all structural or functional equivalents areanticipated to remain within the spirit and scope of the presentlydisclosed systems and methods.

What is claimed is:
 1. A modular rechargeable battery system for use asa replacement of or as an alternative to a conventional lead-acidbattery in a battery-powered industrial forklift truck, said modularrechargeable battery system being adapted to power the battery-poweredindustrial forklift truck, said system comprising: a) a plurality ofbattery modules, wherein each battery module in said plurality ofbattery modules includes a positive terminal and a negative terminal anda plurality of lithium-ion battery cells, said plurality of lithium-ionbattery cells being electrically united within each respective one ofsaid plurality of battery modules to provide a combined electricalpotential between the positive terminal and the negative terminal ofeach respective one of said plurality of battery modules; b) a housinghaving a plurality of compartments, each of said compartments beingconfigured for removably receiving any one of said plurality of batterymodules, said housing being sized and adapted to operatively fit withina battery compartment of the battery-powered industrial forklift truck,wherein each of said plurality of compartments includes a pair of powerconnections for mating connection to the positive terminal and thenegative terminal of any one of said plurality of battery modules whensaid any one is removably received therein; c) said housing furthercomprising electrical conductors and external power terminals, saidexternal power terminals being oriented and adapted for operativeconnection to the electrical power circuitry of the battery-poweredindustrial forklift truck, and said electrical conductors having alayout for connecting electric power from the pairs of power connectionsof the plurality of compartments to said external power terminals; d) aprocessor for monitoring the modular rechargeable battery system and forcontrolling power switches such that operative electrical power isdirected through said electrical conductors to said external powerterminals, said processor being adapted to direct said operativeelectrical power to said external power terminals when fewer than all ofsaid compartments have a corresponding one of said battery modulesoperatively received therein, whereby the battery-powered industrialforklift truck can be provided with operable electrical power when fewerthan all of said compartments have battery modules removably receivedtherein.
 2. The modular rechargeable battery system as defined in claim1 wherein each of said lithium-ion battery cells is interconnected viawire bonding to a printed circuit board (PCB) on a top side of saidlithium-ion battery cells.
 3. The modular rechargeable battery system asdefined in claim 1, wherein said housing is sized and adapted tooperatively fit with a battery compartment of a Class I forklift, andwherein each said battery module weighs 51 pounds or less.
 4. Themodular rechargeable battery system as defined in claim 1 wherein athermally conductive gap-filling material is in thermal contact with abottom surface of said lithium-ion battery cells, wherein said thermallyconductive gap-filling material is not electrically conductive.
 5. Themodular rechargeable battery system as defined in claim 1 wherein saidhousing comprises a plurality of battery module bays, each of saidbattery module bays in said plurality of battery module bays beingconfigured to receive one battery module therein.
 6. The modularrechargeable battery system as defined in claim 5 wherein each of saidbattery module bays is further configured such that said one batterymodule is received within said battery module bay in a verticalorientation.
 7. The modular rechargeable battery system as defined inclaim 5 wherein each of said battery module bays is further configuredsuch that said one battery module is received within said battery modulebay in a horizontal orientation.
 8. The modular rechargeable batterysystem as defined in claim 5 wherein each battery module bay is definedby two lateral partitions and a door on the exterior side of saidhousing, said door having a latch for securing said door in a closedposition, said door further having a hinge and a cooperative pin foropening and closing said door.
 9. The modular rechargeable batterysystem as defined in claim 1 wherein each battery module in saidplurality of battery modules is separately rechargeable.
 10. The modularrechargeable battery system as defined in claim 1 further comprising abattery management system, said battery management system comprising acontroller area network (CAN) configured to receive and monitordiagnostic information from said plurality of battery modules.
 11. Themodular rechargeable battery system as defined in claim 10 wherein saidbattery management system is further configured to enable and disableone or more battery modules during operation of said modularrechargeable battery system based, at least in part, on said diagnosticinformation.
 12. The modular rechargeable battery system as defined inclaim 1 wherein each said battery module includes a pin connector, apositive battery terminal, and a negative battery terminal.
 13. Themodular rechargeable battery system as defined in claim 12 wherein saidpin connector is recessed from a surface of said battery module relativeto said positive and negative battery terminals.
 14. The modularrechargeable battery system as defined in claim 1 wherein saidlithium-ion battery cells are lithium iron phosphate (LFP) batterycells.
 15. The modular rechargeable battery system as defined in claim 1wherein: a) each of said battery modules weighs less than 51 pounds; b)each of said battery modules is separately rechargeable; c) each of saidlithium-ion battery cells is interconnected via wire bonding to aprinted circuit board (PCB) on one side of said lithium-ion batterycells; d) a thermally conductive material is located between a top sideof said lithium-ion battery cell and a top battery tray, between saidtop battery tray and said PCB, and between a bottom side of battery celland a bottom battery tray, wherein said thermally conductive material isnot electrically conductive; e) a thermally conductive gap-fillingmaterial is in thermal contact between the bottom surfaces of thebattery cells and the module enclosure for enabling heat transfer fromthe cells to the enclosure for the purpose of thermal management,wherein said thermally conductive gap-filling material is notelectrically conductive; f) said housing comprises a plurality ofbattery module bays, each of said battery module bays being configuredto receive one battery module therein, each of said battery module baysbeing further configured to receive said one battery module in avertical orientation; g) each said battery module bay is defined by twolateral partitions and a door on the exterior side of said housing, saiddoor having a latch for securing said door in a closed position, saiddoor further having a hinge and a cooperative pin for opening andclosing said door; h) a battery management system comprising acontroller area network (CAN) is configured to: 1) receive and monitordiagnostic information from said plurality of battery modules; and 2)enable and disable one or more battery modules during operation of saidmodular rechargeable battery system based, at least in part, on saiddiagnostic information; i) each said battery module includes a pinconnector, a positive battery terminal, and a negative battery terminal,wherein said pin connector is recessed from a surface of said batterymodule relative to said positive and negative battery terminal; and j)said lithium-ion battery cells are lithium iron phosphate (LFP) batterycells.
 16. The modular rechargeable battery system as defined in claim 1wherein said housing further comprises additional external powerterminals, said additional external power terminals being oriented andadapted for operative connection to an external power source, saidexternal power source providing power for charging said plurality ofbattery modules while said plurality of battery modules are connected tosaid housing.
 17. The modular rechargeable battery system as defined inclaim 11 wherein said battery management system further comprises abattery operating system supervisor (BOSS) module, said BOSS modulebeing configured to enable hot swapping during continuous operation ofthe battery-powered industrial forklift truck.
 18. The modularrechargeable battery system as defined in claim 17 wherein: a) saidhousing further comprises a plurality of battery module bays, each ofsaid battery module bays in said plurality of battery module bays beingconfigured to receive one battery module therein; b) each of saidbattery module bays is further configured such that said one batterymodule is received within said battery module bay in a verticalorientation; c) each battery module bay is defined by two lateralpartitions and a door on the exterior side of said housing, said doorhaving a latch for securing said door in a closed position, said doorfurther having a hinge and a cooperative pin for opening and closingsaid door; d) each said battery module includes a pin connector, apositive battery terminal, and a negative battery terminal; e) said pinconnector includes 5 Volt pin, a CAN HI pin, a CAN LO pin, a ground pin,an identification pin, an interlock pin, a fan power pin, a fan speedpin, and a module ground pin.
 19. A method of controlling a modularrechargeable battery system in a battery-powered industrial forklifttruck comprising: a) a process for enabling hot swapping a module ofsaid modular rechargeable battery system, said process comprising: i)opening a door of a battery module bay; ii) disengaging a positiveterminal and a negative terminal of said battery module from a pair ofpower connections in said battery module bay; iii) removing said batterymodule from said battery module bay using low friction slides orrollers; iv) inserting another battery module into said battery modulebay using low friction slides or rollers; v) engaging a positiveterminal and a negative terminal of said another battery module to saidpair of power connections in said battery module bay; vi) closing saiddoor of said battery module bay and rotating said hinge clockwise aroundsaid cooperative pin.
 20. The method as defined in claim 19 furthercomprising: a) the process for enabling hot swapping a module of saidmodular rechargeable battery system, said process further comprising: i)rotating a hinge counterclockwise around a cooperative pin; ii)disengaging a pin connector of a battery module from a housing, saidhousing comprising a plurality of battery module bays, each of saidbattery module bays in said plurality of battery module bays beingconfigured to receive one battery module therein; iii) engaging a pinconnector of said another battery module to said housing;